* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: "Microsoft YaHei", sans-serif;
    background-color: #f0f0f0;
}

/* 做了最窄的宽度的适配 */
.container { 
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    background-color: #e6f7d0;
    width: 100%;
}

/* 顶部导航栏 */
.header {
    width: 1024px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: white;
    font-size: 1.2em;
    border-bottom: 3px solid #6b9a3a;
    background-image: url("../images/学生成绩管理系统.gif");
    background-repeat: no-repeat;
    background-size: contain;
    height: 150px;
    margin: 0 auto;
}

/* 主内容 */
.main-content {
    display: flex;
    flex: 1;
    overflow: hidden;
    width: 1024px;
    margin: 0 auto;
}

/* 左侧菜单栏 */
.sidebar {
    width: 184px;
    background-color: #d0e8b0;
    padding: 20px;
    border-right: 2px solid #90c54a;
    font-size: 14px;
}

.menu {
    list-style: none;
    line-height: 2em;
}

.menu strong {
    color: red;
    margin-bottom: 10px;
    display: block;
}

.menu li {
    color: #000;
}
.menu a {
    text-decoration: none;
    color: #000;                     /* 设置为黑色 */
    outline: none;
}

.menu a:hover {
    text-decoration: none;
    color: #0066cc;                  /* 悬停时变蓝 */
}

.content-area {
    flex: 1;
    background-color: #e6f7d0;
    display: flex;
    justify-content: center;
    align-items: center;
    background-image: url("../images/主页.gif");
    background-size:cover;
    background-repeat:no-repeat;
}

.placeholder {
    width: 100%;
    height: 100%;
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

/* 底部样式 */
.footer {
    width: 1024px;
    margin: 0 auto;
    background-image: url("../images/底端图片.gif");
    background-repeat: no-repeat;
    background-size: contain;
    background-position: center;
    height: 60px;
    position: relative; /* 关键：开启相对定位 */
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 43px;
    color: black;
    font-size: 12px;
}

.footer h3 {
    margin-bottom: 10px;
    position: absolute; /* 绝对定位 */
    top: 20px;             /* 贴紧顶部 */
    left: 120px;            /* 左侧对齐 */
    z-index: 10;        /* 提升层级，覆盖背景图 */
    color: #000;
    font-size: 14px;
}